[PATCH v3 14/14] buffer: Convert block_truncate_page() to use a folio

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Support large folios in block_truncate_page() and avoid three hidden
calls to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/buffer.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index c38fdcaa32ff..5a5b0c9d9769 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2598,17 +2598,16 @@ int block_truncate_page(struct address_space *mapping,
 			loff_t from, get_block_t *get_block)
 {
 	pgoff_t index = from >> PAGE_SHIFT;
-	unsigned offset = from & (PAGE_SIZE-1);
 	unsigned blocksize;
 	sector_t iblock;
-	unsigned length, pos;
+	size_t offset, length, pos;
 	struct inode *inode = mapping->host;
-	struct page *page;
+	struct folio *folio;
 	struct buffer_head *bh;
 	int err = 0;
 
 	blocksize = i_blocksize(inode);
-	length = offset & (blocksize - 1);
+	length = from & (blocksize - 1);
 
 	/* Block boundary? Nothing to do */
 	if (!length)
@@ -2617,15 +2616,18 @@ int block_truncate_page(struct address_space *mapping,
 	length = blocksize - length;
 	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
 	
-	page = grab_cache_page(mapping, index);
-	if (!page)
+	folio = filemap_grab_folio(mapping, index);
+	if (!folio)
 		return -ENOMEM;
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, blocksize, 0);
+	bh = folio_buffers(folio);
+	if (!bh) {
+		folio_create_empty_buffers(folio, blocksize, 0);
+		bh = folio_buffers(folio);
+	}
 
 	/* Find the buffer that contains "offset" */
-	bh = page_buffers(page);
+	offset = offset_in_folio(folio, from);
 	pos = blocksize;
 	while (offset >= pos) {
 		bh = bh->b_this_page;
@@ -2644,7 +2646,7 @@ int block_truncate_page(struct address_space *mapping,
 	}
 
 	/* Ok, it's mapped. Make sure it's up-to-date */
-	if (PageUptodate(page))
+	if (folio_test_uptodate(folio))
 		set_buffer_uptodate(bh);
 
 	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
@@ -2654,12 +2656,12 @@ int block_truncate_page(struct address_space *mapping,
 			goto unlock;
 	}
 
-	zero_user(page, offset, length);
+	folio_zero_range(folio, offset, length);
 	mark_buffer_dirty(bh);
 
 unlock:
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 
 	return err;
 }
-- 
2.39.2